U.S. patent application number 11/346755 was filed with the patent office on 2007-08-09 for soft-stop braking control.
Invention is credited to Douglas Charles Osborn, James Andrew Techentin.
Application Number | 20070182243 11/346755 |
Document ID | / |
Family ID | 38333326 |
Filed Date | 2007-08-09 |
United States Patent
Application |
20070182243 |
Kind Code |
A1 |
Osborn; Douglas Charles ; et
al. |
August 9, 2007 |
Soft-stop braking control
Abstract
A method is provided for applying a soft-stop control to the
vehicle brake actuators of a vehicle during a vehicle stop
operation. A brake apply operation is detected. A determination is
made whether the vehicle speed is below a first threshold stopping
speed. Braking pressure to the vehicle actuators is reduced as a
function of vehicle speed, vehicle deceleration, and brake apply
pressure if the vehicle speed is below the first threshold stopping
speed.
Inventors: |
Osborn; Douglas Charles;
(Royal Oak, MI) ; Techentin; James Andrew;
(Hartland, MI) |
Correspondence
Address: |
MACMILLAN, SOBANSKI & TODD, LLC
ONE MARITIME PLAZA - FOURTH FLOOR
720 WATER STREET
TOLEDO
OH
43604
US
|
Family ID: |
38333326 |
Appl. No.: |
11/346755 |
Filed: |
February 3, 2006 |
Current U.S.
Class: |
303/10 |
Current CPC
Class: |
B60T 2201/02 20130101;
B60T 8/00 20130101; B60T 7/22 20130101; B60T 2230/04 20130101 |
Class at
Publication: |
303/010 |
International
Class: |
B60T 13/16 20060101
B60T013/16 |
Claims
1. A method for applying a soft-stop control to the vehicle brake
actuators of a vehicle during a vehicle stop operation, said method
comprising the steps of: detecting a brake apply operation;
determining if the vehicle speed is below a first threshold
stopping speed; and reducing braking pressure to said vehicle brake
actuators as a function of vehicle speed, vehicle deceleration, and
brake apply pressure if said vehicle speed is below said first
threshold stopping speed.
2. The method of claim 1 further comprising the step on determining
if a secondary braking function is active, wherein said step of
reducing said braking pressure is discontinued if a secondary
braking function is active during said brake apply operation.
3. The method of claim 2 wherein said secondary braking function
includes an anti-lock braking function.
4. The method of claim 2 wherein said secondary braking function
includes a corner brake control function.
5. The method of claim 2 wherein said secondary braking function
includes a deceleration based isolation function.
6. The method of claim 1 further comprising the step of sensing for
a target proximate to said vehicle, wherein said step of reducing
said braking pressure is discontinued if a target is sensed within
a target distance threshold of said vehicle.
7. The method of claim 6 wherein said target is sensed forward of
said vehicle.
8. The method of claim 6 wherein said target is sensed rearward of
said vehicle.
9. The method of claim 1 wherein said step of reducing said braking
pressure is discontinued if said vehicle speed is less than a
second threshold stopping speed.
10. The method of claim 1 wherein said step detecting a brake apply
operation comprises sensing said master cylinder pressure greater
than a predetermined stop pressure threshold.
11. The method of claim 1 wherein said step detecting a brake apply
operation comprises sensing an activation of a brake switch.
12. The method of claim 1 wherein said step detecting a brake apply
operation comprises sensing a travel of a brake pedal greater than
a predetermined brake pedal distance threshold.
13. The method of claim 1 wherein said step of reducing said
braking pressure is discontinued if a rate of change of said brake
apply pressure is outside of a predetermined braking rate
threshold.
14. The method of claim 13 wherein said rate of change of said
brake apply pressure is determined by sensing a rate of change of
said master cylinder pressure.
15. The method of claim 13 wherein said rate of change of said
brake apply pressure is determined by sensing a change in a travel
distance of a brake pedal.
16. A method for applying a soft-stop control to the vehicle brake
actuators of a vehicle during a vehicle stop operation, said method
comprising the steps of: detecting a brake apply operation by a
driver in response to a master cylinder pressure being above a
predetermined braking rate threshold; determining that a secondary
brake operation is inactive; determining that a vehicle speed is
between a first threshold stopping speed and a second threshold
stopping speed; and reducing brake pressure to said vehicle brake
actuators as a function of said master cylinder pressure, said
vehicle speed, and a vehicle deceleration if said secondary brake
operation is inactive and said vehicle speed is between said first
and second threshold stopping speed.
17. The method of claim 16 further comprising the step of sensing
for a target proximate to said vehicle, wherein said step of
reducing said braking pressure to said vehicle brakes is
discontinued if a target is sensed rearward of said vehicle is
within a target distance threshold.
18. The method of claim 16 wherein said step of reducing said
braking pressure is discontinued if a rate of change of said brake
pressure is outside of a predetermined braking rate threshold.
19. A method for applying a soft-stop control to the vehicle brake
actuators of a vehicle during a vehicle stop operation, said method
comprising the steps of: detecting a brake apply operation by an
activation of a brake switch; determining that a secondary brake
operation is inactive; determining that a vehicle speed is between
a first threshold stopping speed and a second threshold stopping
speed; and reducing brake pressure to said vehicle brake actuators
as a function of said master cylinder pressure, said vehicle speed,
and a vehicle deceleration if said secondary brake operation is
inactive and said vehicle speed is between said first and second
threshold stopping speed.
20. A method for applying a soft-stop control to the vehicle brake
actuators of a vehicle during a vehicle stop operation, said method
comprising the steps of: detecting a brake apply operation by
sensing a travel of a brake pedal greater than a predetermined
brake pedal travel threshold; determining that a secondary brake
operation is inactive; determining that a vehicle speed is between
a first threshold stopping speed and a second threshold stopping
speed; and reducing brake pressure to said vehicle brake actuators
as a function of said master cylinder pressure, said vehicle speed,
and a vehicle deceleration if said secondary brake operation is
inactive and said vehicle speed is between said first and second
threshold stopping speed.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] Not Applicable
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not Applicable
REFERENCE TO A SEQUENCE LISTING, A TABLE, OR A COMPUTER PROGRAM
LISTING COMPACT DISC APPENDIX
[0003] Not Applicable
BACKGROUND OF THE INVENTION
[0004] 1. Field of the Invention
[0005] This invention relates in general to vehicle braking, and
more specifically, to gradual vehicle braking.
[0006] 2. Description of the Related Art
[0007] For vehicle braking systems using a manually applied vacuum
braking system or boost assist braking system, pressurized
hydraulic braking fluid is applied to the vehicle brake actuators
as demanded by the drivers braking demand input. That is, a
proportional braking force is applied to the vehicle brake
actuators in response to the driver's force exerted on the brake
pedal. Applying too much braking pressure to the brake pedal during
an end of stop operation may lead to a sudden jolt or jerk stop
(i.e., wrap-up) as the vehicle comes to a complete stop. This
typically occurs when the driver fails to relieve braking pressure
to the vehicle brake pedal so as to ease off the pressure applied.
The wrap-up is displeasing to passengers traveling in a vehicle as
it is for the driver of a vehicle. As a result, bringing the
vehicle to a gradual stop has been entirely dependent upon the
driver's actions of applying just the right amount of force to the
vehicle brake pedal by manually easing off the brake pedal so as to
reduce wrap-up at the end of stop operation.
BRIEF SUMMARY OF THE INVENTION
[0008] The present invention has the advantage of eliminating a
hard stop (wrap-up) during an end of the stop braking operation
that is most common when the driver is applying more than the
required braking pressure to stop the vehicle and fails to reduce
brake pressure to the vehicle brake actuator as the vehicle comes
to a complete stop. The present invention also has the advantage of
monitoring other factors such as secondary braking functions and
target sensing to discontinue a soft-stop braking routine and allow
for full control of vehicle braking by the driver or for the
application of secondary braking operations.
[0009] In one aspect of the present invention, a method is provided
for applying a soft-stop control to the vehicle brake actuators of
a vehicle during a vehicle stop operation. A brake apply operation
is detected. A determination is made whether the vehicle speed is
below a first threshold stopping speed. Braking pressure to the
vehicle actuators is reduced as a function of vehicle speed,
vehicle deceleration, and brake apply pressure if the vehicle speed
is below the first threshold stopping speed.
[0010] Various objects and advantages of this invention will become
apparent to those skilled in the art from the following detailed
description of the preferred embodiment, when read in light of the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a schematic of a vehicle soft-stop system of the
present invention.
[0012] FIG. 2 is a flowchart for a method for a soft-stop routine
of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0013] Referring now to the Drawings and particularly to FIG. 1,
there is shown a schematic diagram of a vehicle and its associated
hydraulic braking system and target sensing system. The vehicle is
shown generally at 10 and includes vehicle wheels 11a, b, c, d. The
hydraulic braking system includes vehicle brake actuators 12a, b,
c, d with each vehicle brake actuator including a respective brake
actuation member (slave cylinder) and friction member actuable by
the actuation member for engaging a rotatable braking surface of
the vehicle wheels 11a, b, c, d respectively. Braking fluid
circuits 14, 16, 18, 20 provide braking fluid from a source of
pressurized brake fluid such as a manually operated master cylinder
22 for pressurizing vehicle brake actuators 12a, b, c, d
respectively.
[0014] A vehicle brake control module 24 may be used in cooperation
with the master cylinder 22 to provide primary braking functions
(i.e., as demanded by a driver) and secondary braking functions
(i.e., automated vehicle stability control functions). Various
hydraulically controlled valves (not shown) within the brake
control module 24 control the hydraulic pressure to the four
vehicle brake actuators 12a, b, c, d either independently or in
combination for performing various deceleration or stability
control operations. A pressure sensor 25 is coupled to at least one
fluid circuit for sensing hydraulic pressure output from the master
cylinder 22 via the respective fluid circuit.
[0015] Secondary braking functions are invoked for maintaining a
function of vehicle stability control. Such secondary braking
functions are automatically implemented in response to either a
driver's brake apply demand when vehicle stability issues are
occurring (e.g., ABS functionality) or when a vehicle encounters
stability control problems without a driver's braking apply demand
(e.g., traction control functionality). Other secondary braking
functions may include vehicle stability control functionality
(VSC), yaw stability control functionality (YSC), corner brake
control (CBC), dynamic rear proportioning (DRP), and deceleration
based isolation (DBI).
[0016] The vehicle 10 is also shown to include a target proximity
sensing system 26. The target is meant to include a person,
vehicle, moving or stationary object detectable by the target
proximity sensing system 26. The target proximity sensing system 26
may include a forward target sensing unit 28, such as an adaptive
cruise control system (ACC) sensor. The ACC typically includes a
radar sensor that senses the proximity of a target forward of the
vehicle 10. The target proximity sensing system 26 may also include
a rear proximity sensing unit 32 that senses targets rearward of
the vehicle 10 such as backup sensors for detecting such targets as
a person, vehicle, or object.
[0017] The brake control module 24 also controls the soft-stop
control functions of the present invention. Soft-stop control
functions automatically reduce braking pressure during a vehicle
stop when the vehicle is within a predetermined speed range for
bringing the vehicle to a gradual stop while avoiding a hard stop
jerk that is typically the result of a driver having more pedal
pressure than that which is required to stop the vehicle in a
reasonably short distance when braking. Soft-stop would only be
applied to vehicle stops made without the assistance of other forms
of secondary braking control functions being active (e.g., ABS
active). The intent is to eliminate the sudden end of a stop
wrap-up by reducing braking pressure by 25-75%.
[0018] To activate the soft-stop algorithm, the braking control
unit 24 must detect a brake apply operation and the vehicle speed
must be between a first threshold stopping speed and a second
threshold stopping speed. The brake apply operation may be detected
by a brake switch, the master cylinder pressure being greater than
a predetermined stop pressure threshold, or sensing the travel of
the brake pedal beyond a predetermined brake pedal distance
threshold. Requiring the vehicle speed to be below the first
threshold stopping speed, typically between 3 and 10 mph, allows
the vehicle to be stopped within the substantially same stopping
distance as intended by the driver. Otherwise, reducing pressure to
the vehicle brake actuators while the vehicle has too much inertia
may lead to the vehicle stopping significantly beyond the drivers
intended stopping location. The intention of the soft-stop routine
is to eliminate the vehicle wrap-up while substantially maintaining
the intended stopping distance as intended by the driver.
[0019] In addition to the above conditions being met, all secondary
braking functions must be inactive. If any secondary braking
function is active, then the brake control module 24 will not
activate the soft-stop routine. In addition, if any secondary
braking function becomes active while the soft start routine is
active, the brake control module 24 will deactivate the soft-stop
routine as secondary braking operations take priority over the
soft-stop functions.
[0020] The brake control unit 24 is also in communication with the
target proximity sensing system 26. When the soft-stop routine is
activated or prior to the soft-stop routine being activated, sensed
outputs from the target proximity sensing system 26 are provided to
the brake control module 24 for sensing the proximity of a target
forward or rearward of the vehicle 10. If at any time a target as
sensed by the target proximity sensing system 26 is within a target
distance threshold, then the soft-stop routine is deactivated (if
presently in an activation state) or is prevented from being
activated (if presently in a deactivation state).
[0021] When the soft-stop routine is activated, the brake control
module 24 modulates (e.g., energizes and de-energizes) respective
hydraulically controlled valves for reducing hydraulic pressure to
the vehicle brake actuators 12a,b,c,d for gradually bringing the
vehicle to a gradual stop without wrap-up at the end of stop
operation. If a secondary braking function becomes active, or a
target is sensed within the target distance threshold, or the
master cylinder pressure below the predetermined stop pressure
threshold while the soft start routine is active, then the
soft-stop routine is immediately deactivated and full braking apply
control as demanded by the driver is applied. For example,
activation of a secondary braking operation would indicate that a
stability control issue is occurring and the brake control module
24 is currently attempting to correct the condition.
[0022] Another example of which would deactivate the soft-stop
routine includes sensing a target in the trajectory travel path of
the vehicle within the target distance threshold. For safety
purposes, the soft-stop routine is discontinued to allow the driver
to perform an immediate stop, if required.
[0023] Yet another example of which would deactivate the soft-stop
routine includes sensing a drop in the master cylinder pressure
below a predetermined pressure threshold. Such a pressure reduction
in the master cylinder would indicate the driver is attempting to
intentionally relieve braking pressure. The soft-stop routine would
be discontinued and full braking apply control is provided to the
driver.
[0024] Once the vehicle is traveling less than the second threshold
stopping speed, typically 2-5 mph, wrap-up is no longer an issue
and full braking control is provided to the driver. This allows the
driver to have full control over the brake pressure applied to the
brake actuators for maintaining the vehicle in a stopped position
as intended by the driver. The advantage is to reduce the braking
pressure applied to the vehicle brakes actuators while the vehicle
is traveling within a predetermined for eliminating wrap-up.
[0025] FIG. 2 is a method for applying a soft-stop braking routine
during an end of stop operation. In step 41, a routine is initiated
for determining whether to activate a soft-stop algorithm. In step
42, a determination is made whether the vehicle brakes have been
applied by the driver of the vehicle. A brake apply operation by
the driver is typically sensed by a brake switch being actuated, or
by sensing of the brake pedal travel beyond a predetermined pedal
distance travel, or when the master cylinder pressure is above a
predetermined pressure threshold. Pressure output by the master
cylinder being above a predetermined pressure threshold could
indicate that that pressure is being applied to the vehicle brakes
but due to an inoperable brake switch or brake pedal travel sensor,
the system has not identified the brake apply operation. If either
the brake switch, braking pedal travel sensor, or master cylinder
pressure does not indicate a brake apply operation is being
demanded by the driver, then the routine is exited in step 57. If
the determination is made in step 42 that a brake apply operation
is occurring, then a determination is made whether any secondary
braking functions are active.
[0026] In step 43, a determination is made whether an anti-lock
braking function is active. If the anti-lock braking function is
active, then the routine is exited in step 57. If the anti-lock
braking function is inactive, then the routine proceeds to step
44.
[0027] In step 44, a determination is made as to whether the corner
brake control function is active. If the corner brake control
function is active, then the routine is exited in step 57. If the
corner brake control function is inactive, then the routine
proceeds to step 45.
[0028] In step 45, a determination is made whether the front
deceleration based isolation function is active. If the front
deceleration based isolation function is active, then the routine
is exited in step 57. If the front deceleration based isolation
function is inactive, then the routine proceeds to step 46.
[0029] In step 46, a determination is made whether the vehicle
speed is less than the first threshold stopping speed. The first
threshold speed may be a predetermined value, or may be calculated
as a function of the vehicle's rate of deceleration. If the vehicle
speed is greater than the first threshold stopping speed, then the
routine is exited in step 57. If the vehicle speed is less than the
first threshold stopping speed, then the routine proceeds to step
47.
[0030] In step 47, a determination is made whether the rate of
change of the driver's braking effort (brake apply pressure) is
within a predetermined braking rate threshold. A rate of change
greater than the predetermined braking rate threshold indicates
that the driver is increasing braking efforts faster than what is
typically expected and it is determined that the driver's intent is
to stop the vehicle immediately. A rate of change less than the
predetermined braking rate threshold indicates that the driver
braking efforts are decreasing (i.e., while the vehicle speed is
below the first threshold speed) and it is determined that the
driver is relieving braking pressure intentionally to manually
perform a soft stop. The braking efforts of the driver can be
determined by the master cylinder pressure or brake pedal travel.
If the determination is made that the rate of change of the
driver's braking effort is outside of the predetermined braking
rate threshold, then the routine is exited via step 53. If the
braking effort is within the predetermined braking rate threshold,
then the routine proceeds to step 48.
[0031] In step 48, a determination is made whether the vehicle is
traveling in a forward direction. If the vehicle is traveling in a
forward direction, then a determination is made in step 51 as to
whether a target is within the forward trajectory path of the
vehicle and whether the target is within a target distance
threshold. If the target is within the target distance threshold,
then the routine is exited in step 57. If the target is not within
the target distance threshold, then the routine proceeds to step 52
where the soft start algorithm is activated.
[0032] In step 48, if the determination is made that the vehicle is
not traveling in a forward direction, then a determination is made
in step 49 as to whether the vehicle is traveling in a rearward
direction. If the vehicle is not traveling in the rearward
direction, then the vehicle may be already stopped which would not
require the activation of the soft-stop algorithm. The routine is
then exited in step 57. If the vehicle is traveling in a rearward
direction, then a determination is made in step 50 as to whether a
target is sensed by the rear target sensing unit and if the target
is within a target threshold distance. If the determination is made
that the target is within the target distance threshold, then the
routine is exited in step 57. If the determination is made in step
50 that the target is not within the target distance threshold,
then the soft start algorithm is activated in step 52.
[0033] In step 53, a determination is made as to whether the
vehicle speed is greater than that a second threshold stopping
speed. The second threshold speed may be a predetermined value, or
may be calculated as a function of the vehicle's rate of
deceleration. The inertia of the vehicle must be at least at a
minimum speed for the soft-stop control to be effective, otherwise,
soft-stop will have little or no advantageous effect on the end of
stop operation. As a result, a vehicle traveling at a speed less
than the second threshold stopping speed will not utilize soft-stop
operation or discontinue use of the soft-stop operation. The
routine is then exited via step 55. An end of stop (EOS) is
activated in which full braking control is returned to the driver's
control in step 55.
[0034] If the determination is made in step 53 that the vehicle
speed is greater than the second threshold stopping speed, then a
determination is made in step 54 whether the rate of change of the
driver's braking effort is greater than the predetermined braking
rate threshold which would indicate that the driver is increasing
the braking pressure to abruptly stop the vehicle instead of softly
stopping the vehicle. If the determination is made that the rate of
change of the driver's braking effort is greater than the
predetermined braking rate threshold, then the routine is exited
via step 55. If the rate of change of the braking effort is not
greater than the predetermined braking rate threshold, then the
braking pressure to the vehicle brake actuators are reduced,
typically by 25-75%, in step 56 for performing a soft-stop
operation to the vehicle.
[0035] After braking pressure is reduced in step 56, the routine
returns to step 53 to continuously check vehicle speed and the
driver's braking efforts, respectively, for maintaining a reduced
braking pressure. The reduced braking pressure can be a continued
reduction in pressure or the holding of the targeted pressure. If
the determination is made in step 53 that the vehicle speed is less
than the second threshold stopping speed, then full the soft-stop
algorithm is discontinued and full braking control is returned to
the driver's control in step 55. This allows the driver to have
full control over the brake pressure applied to the brake actuators
for maintaining the vehicle in a stopped position. The routine is
exited in step 57.
[0036] In accordance with the provisions of the patent statutes,
the principle and mode of operation of this invention have been
explained and illustrated in its preferred embodiment. However, it
must be understood that this invention may be practiced otherwise
than as specifically explained and illustrated without departing
from its spirit or scope.
* * * * *